Fire Alarm Circuits Have No Style

Readers of the National Fire Protection Association’s (NFPA) 72 2010, the National Fire Alarm and Signaling Code, will find many changes including three new chapters. One of the new chapters is dedicated to circuits and pathways.

Professionals in the field will remember that, since the 1993 edition of the code, they have had to deal with both classes and styles of circuits.

As explained in the annex and as found in previous editions of the code, “initiating device circuit, signaling line circuit, and notification appliance circuit performance class/style tables were rooted in ‘copper’ wiring methods. Increasingly, fire alarm control units today use new communication technologies, such as Ethernet, optical fiber cable and wireless. These technologies do not fit in the category of ‘copper’ wiring methods.” The code now uses the terms circuits and pathways to acknowledge the use of these new technologies.

NFPA 72 2010 has eliminated styles of circuits. Instead, the code designates circuits and pathways as Class A, Class B, Class C, Class D, Class E or Class X, depending on their performance.
The code states that “the intent of the circuit designations is not to create a hierarchal ranking; rather it is to provide guidance on the levels of performance.” For those who need to cross-reference the performance of previous classes and styles of circuits, NFPA 72 2010 has the initiating device circuit, signaling line circuit and notification appliance circuit performance class/style tables from previous editions of the code included as tables in Annex A.

The code describes the performance of each pathway as follows:

• Each Class A pathway includes a redundant path. The pathway’s operational capability continues past a single open fault. And, the fire alarm control unit (FACU) annunciates any conditions that affect the intended operation of the path.

• Each Class B pathway does not include a redundant path. Its operational capability stops at a single open. And, the FACU annunciates any conditions that affect the intended operation of the path.

• Each Class C pathway includes one or more paths where end-to-end communications verifies the operational capability of the total pathway. But, the FACU does not monitor the integrity of individual paths. The FACU does annunciate a loss of end-to-end communication. Please note that the Class C reference is new and is intended to describe technologies that monitor the integrity of the communication pathway by polling or continuous communication “handshaking.” Examples of Class C pathways include the following: “(1) Fire control unit or supervisory station connections to a wired LAN, WAN, or Internet”; “(2) Fire control unit or supervisory station connections to a wireless LAN, WAN, and Internet”; “(3) Fire control unit or supervisory station connections to a wireless (proprietary communications)”; and “(4) Fire control unit digital alarm communication transmitter or supervisory station digital alarm communication receiver connections to the public switched telephone network.”

• Each Class D pathway provides fail-safe operation. The FACU does not annunciate faults. But, the pathway does perform the intended operation in the event of a pathway failure. Examples of these circuits or pathways include circuits that provide power to door holders, where interruption of the power results in the door closing. It also includes circuits that provide power to locking hardware that release upon an open circuit or contact operation within the FACU.

• Class E designates those pathways where the FACU does not need to monitor the pathway for integrity, as described in Section 10.17 of the code.

• Each Class X pathway includes a redundant path. Its operational capability continues past a single open or short circuit. The FACU annunciates conditions that affect the intended operation of the path. This new designation intends to apply to signaling line circuit pathways described in previous editions of the code as “Style 7.”

Of course, NFPA 72 2010 also requires that the installation of all pathway wiring, cable and equipment—including all circuits controlled and powered by the fire alarm system and the means by which fire alarm circuits enter or exit buildings—meet the requirements of NFPA 70, the National Electrical Code (NEC).

Additionally, optical fiber cables installed as part of the fire alarm system must meet the requirements of NEC Article 770. The method of installation for optical fiber cables must protect the cables against physical damage in accordance with the NEC Article 760.

The installation of all system wiring should always account for the system manufacturer’s published installation instructions as well as any limitations of the applicable product listings or approvals.
Obviously, the code has changed drastically in the way it designates wiring or pathways. Professional contractors absolutely must read and understand these changes and the appropriate way to use each pathway in a fire alarm system installation.

MOORE, a licensed fire protection engineer, frequent speaker and an expert in the life safety field, is a co-editor of the current National Fire Alarm Code Handbook. Moore is a principal with Hughes Associates Inc. at the Warwick, R.I., office.

Wayne D. Moore, a licensed fire protection engineer, frequent speaker and an expert in the life safety field, is a principal member and past chair of NFPA 72, Chapter 24. Moore is a vice president with JENSEN HUGHES at the Warwick, R.I., office. He c...

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